A holding material for a catalytic converter (hereinafter also referred to as a “holding material”) is obtained by wet molding an aqueous slurry containing inorganic fibers and an organic binder by using a dehydration forming die having a specific shape, followed by hot pressing. Then, the holding material is incorporated in a metal casing in a state where it is mounted on a catalyst carrier (hereinafter also referred to as “canning”). The organic binder contained in the holding material is burnt down by heat applied after canning, and the inorganic fibers restricted by the organic binder in a compressed state expands in a thickness direction, thereby sealing a gap between the catalyst carrier and the casing and holding the catalyst carrier.
On the other hand, with a progress of floor lowering of automobiles, it has been studied to decrease a space necessary for installation of the catalytic converter by changing the cross-sectional shape of the catalyst carrier incorporated under floor from a perfect circle to a flattened shape, that is to say, an ellipse or a track shape. However, heat transfer in the catalyst carrier becomes uneven, or residual stress in a production process of the casing varies with respect to a place of the casing in some cases. Accordingly, after canning, a partial difference in thermal expansion occurs in the casing, resulting in an uneven degree of expansion. As a result, the gap difference between the catalyst carrier and the casing becomes uneven, and sealability or holding force of the holding material is impaired at a place more largely expanded.
As a holding material for this flattened catalyst carrier, there is proposed a holding material in which a portion in contact with an outer circumferential surface in a minor-axis direction of the catalyst carrier is thicker than a portion in contact with an outer circumference in a major-axis direction (see JP-UM-A-59-39719).